Jason Day has challenged himself to "get out of his own way" and stop complicating major championship Sundays.
The former world No.1 owns four top-10 results since his breakthrough major title at the 2015 US PGA Championship and is eyeing another chance at the year's final major.
Day struggled to hit top gear during a three-under-par 67 but shares sixth at eight-under alongside five others including defending champion Justin Thomas (68) and golf great Tiger Woods (66) at Missouri's Bellerive Country Club.
At 12 under, two-time US Open winner Brooks Koepka (66) will take a two-shot lead into the final round over Australian Adam Scott (65) - with the pair to comprise the final group.
Day, who finished second by one shot at the 2016 PGA Championship and tied for ninth last year, knows what has been missing his 2015 triumph.
"If I can get out of my own way and just play, don't think about anything else," Day told AAP when asked what needs to change.
"If it's not going my way early, I can't force things or get carried away."
With the big-hitting Koepka in career-best form and eyeing his second major of the year, Day said he will need to fire on all cylinders to have a chance.
"Everything will need to be sharp but if I have to pick one it will be driving and putting," Day said.
Day arrived at Bellerive with two US PGA Tour wins under his belt this year and a tie for 10th at last week's elite WGC-Bridgestone Invitational.
Although he expected to be higher up the leaderboard in St. Louis, the Queenslander has no doubt he can go low and leave himself a chance at victory.
"Definitely, I think there are low scores in me tomorrow," Day said.
"I don't think someone's going to run away with it tomorrow; it's still a major championship."